In an image forming apparatus such as a copying machine, an image on an original is read, an electrostatic latent image corresponding to the read image is formed on a surface of a photosensitive drum, the electrostatic latent image is developed into a visible image, and the visible image is printed on a copying paper sheet. A great number of copying sheets are contained in a paper feed cassette, and the copying sheets are taken out of the feed cassette one by one and fed to the photosensitive drum.
In the case of an image forming apparatus having a double-side print mode function, read images can be printed on both an obverse surface and a reverse surface of a sheet taken out of the paper feed cassette.
Specifically, in the double-side print mode, a copying sheet taken out of the paper feed cassette is fed to the photosensitive drum in the state in which the obverse surface of the sheet comes in contact with the surface of the photosensitive drum. At this time, an image read from a first original is formed as a visible image on the surface of the photosensitive drum, and the visible image is transferred onto the obverse surface of the copying sheet. The copying sheet, on which the visible image has been transferred, is separated from the photosensitive drum. The separated copying sheet is fed to a heat roller. The heat roller heats the copying sheet and fixes the image transferred on the obverse surface of the copying sheet.
The copying sheet, which has come out of the heat roller, is reversed by a sheet convey mechanism called xe2x80x9cADU,xe2x80x9d and returned to a convey path located upstream of the photosensitive drum. The returned copying sheet is fed once again to the photosensitive drum in the state in which the reverse surface of the sheet comes in contact with the surface of the photosensitive drum. At this time, an image read from a second original is formed as a visible image on the surface of the photosensitive drum, and the visible image is transferred onto the surface of the copying sheet. The copying sheet, on which the visible image has been transferred, is separated from the photosensitive drum. The separated copying sheet is output to an output tray via the heat roller.
When the copying sheet is conveyed and fed to the photosensitive drum, there may be a case where the position of the copying sheet is slightly displaced from a standard position (proper position) in a direction perpendicular to the direction of conveyance of the copying sheet.
In particular, in the image forming apparatus having the double-side print mode function, one copying sheet is twice fed to the photosensitive drum, and the copying sheet may be displaced each time it is fed. If the copying sheet is fed to the photosensitive drum with the displacement, the positions of images printed on both sides of the copying sheet are displaced from the proper position in the direction perpendicular to the direction of conveyance of the copying sheet.
The object of the present invention is to provide an image forming apparatus and a method of controlling the apparatus, wherein images can always be printed on obverse and reverse surfaces of a copying paper sheet at proper positions.
The present invention provides an image forming apparatus wherein a first image is formed on an image carrying body, a paper sheet is fed to the image carrying body and thereby the first image on the image carrying body is printed on one surface of the paper sheet, and a second image is formed on the image carrying body, the paper sheet, which has come out of the image carrying body, is reversed and fed once again to the image carrying body and thereby the second image on the image carrying body is printed on the other surface of the paper sheet, the apparatus comprising:
a control section for shifting a formation position of the first image on the image carrying body by a first set amount, relative to a predetermined reference position, in a direction perpendicular to a direction of conveyance of the paper sheet; and
a control section for shifting a formation position of the second image on the image carrying body by a second set amount, relative to a predetermined reference position, in the direction perpendicular to the direction of conveyance of the paper sheet.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.